SE439510B - BINDING AGENTS FOR THE PREPARATION OF Aqueous COMPOSITIONS FOR COATING PAPER, PAPER AND CARTON FOR PRINTING - Google Patents

Description

7804605-9 agents, the most important of which are tetrasodium pyrophosphate, sodium hexametaphosphate, low molecular weight polyacrylates, in amounts between 0.2 and 0.5% by weight relative to the amount of pigment. These adhesives are bonded to the paper, cardboard or cardboard using adhesive. An aqueous latex of a synthetic polymer, such as a copolymer of butadiene and styrene, a carboxylated copolymer of butadiene and styrene, an acrylic polymer or a polymer of vinyl acetate, used either alone or in admixture with natural binders, is generally used. , such as starch, proteins, casein or synthetic binders, such as polyvinyl alcohols. It is also possible to use together with the latex products which can improve the water retention properties of the coating compositions, for example carboxymethylcellulose or alginates.

The coating compositions may further contain other constituents of various kinds, such as in particular crosslinking agents (crosslinking agents), antifoaming agents, lubricants, optical brighteners (optical blue agents), dyes.

Coating of paper, cardboard and cardboard by means of the aqueous compositions is carried out by means of a coating machine according to various methods, using various kinds of devices among which may be mentioned those known in the industry under the following designations: air knife, glue press , Champion coating device, Massey coating device, trailing squeegee.

After coating, the paper, cardboard or board is subjected to a drying operation. The properties of the coated paper, paperboard or board vary according to the printing method for which the products are intended, of which heliogravure printing and offset printing are the two most important. The resistance to dry abrasion, which is representative of the adhesion of the coating to the substrate, should be better the more viscous the ink. Furthermore, when quadrichrome offset printing is required, the second, third or fourth color must be printed on a pre-moistened or softened substrate. In order to avoid the phenomenon of napping in the moist state, which causes soiling of the cloth and the offset presses, it is therefore important that the paper, cardboard or board shows sufficient resistance to napping in the wet state. In order to achieve the levels of resistance to dry and wet picking required for the printing method, it is desirable to use the least possible amount of binder, since in general the more the amount of binder used is increased, the more the optical properties, whiteness deteriorates and gloss, which is specifically provided by the pigment.

Among the synthetic polymer latex materials used as binders, therefore, those which exhibit the suede bonding ability are the most interesting, since these, which can be used in the least amount to obtain the level of resistance to dry napping required for the printing method, make it possible to obtain maximum whiteness. and brilliance.

The binders according to the invention are based on an aqueous latex of a synthetic polymer in which the content of water-soluble compounds dissolved in the aqueous phase is less than 0.5% by weight relative to the amount of polymer.

The water-soluble compounds essentially comprise salts which, for example, consist of catalyst residues, surfactants and macromolecular compounds, for example carboxylated compounds.

According to the invention, it has been found that, if all other conditions are unchanged, the binders in which the content of water-soluble compounds dissolved in the aqueous phase is sufficiently low show improved binding capacity.

As synthetic polymers used in the form of latex according to the invention, there may be mentioned copolymers of butadiene and styrene, carboxylated copolymers of butadiene and styrene, polyvinyl acetates, carboxylated polyvinyl acetates, copolymers of vinyl acetate and alkyl acrylate; -9 acrylate.

The determination of the content of water-soluble compounds dissolved in the aqueous phase of the latex is carried out by the method described below which utilizes the properties of the semipermeable membranes with elevated separation threshold which allow the passage of low molecular weight compounds and, if necessary, carboxylated macromolecular compounds and retains the polymer particles.

The latex to be examined, which has a known dry matter weight content tl, expressed as%, is subjected to an ultrafiltration operation by passing through a laboratory-type ultrafiltration module equipped with a semipermeable membrane marketed by Rhone-Poulenc Industries under the designation _ " Iris 3538 ". The weight content of dry matter is determined in the first drop of permeate which is collected, tp, expressed in%, which is equal to the weight content of the aqueous phase of the latex.

The content of the water-soluble compounds dissolved in the aqueous phase ts, expressed in%, in relation to the polymer weight, is given by the formula: 100 - tp <tl) tl The preparation of a latex useful as a binder according to the invention is generally carried out is known to be useful in the preparation of aqueous compositions for coating paper, paperboard and board for printing and which can be prepared by any of the per se known methods of polymerizing water emulsion, by removing a sufficient amount of the water-soluble compounds from latexen. This removal can be performed, for example, by ultrafiltration through a semipermeable membrane. During the ultrafiltration, the compounds dissolved in the aqueous phase pass through the membranes of the permeate while a gradual desorption and elimination of the water-soluble compounds which are adsorbed on the surface of the latex particles is obtained. The ultrafiltration operation can be carried out in a conventional plant, for example of the type found in industry.

Such a plant is shown in the accompanying drawing figure, which shows the plant partly in vertical section. The plant essentially comprises a container 1 containing the latex to be treated, a container 2 containing deionized water, an ultrafilter 3 and a pump 4. The container 2, which opens into the container 1, ensures the supply of deionized water to the latter through a line. 5 and an automatic valve 6 actuated by a float 7, which ensures the maintenance of a constant level of the bath in the container 1. The pump 4 provides feeding of the latex through a line 8 to the ultrafilter 3. Through a line 9, in which a quantity meter 10, the concentrate delivered by the ultrafilter 3 is returned in circulation to the container 1. A pipe loop 11 for circulation of heat exchanger fluid is immersed in the latex in the container 1 and enables constant maintenance of its temperature. A line 12 is used to start up the plant.

The system further also includes shut-off valves 13, 14, 15, 16 and 17 as well as manometers 18 and 19.

The plant is started and the procedure is carried out as follows: With the valve 14 closed and the valve 13 open, the pump 4 is started, after which the valves 14 and 15 are opened and the valve 13 is closed.

By gradual adjustment, the opening of the valves 14 and 15 is controlled in such a way as to obtain the desired supply of latex under the desired pressure, the pressure difference indicated by the manometers 18 and 19 representing the material loss through the ultrafilter 3.

For a satisfactory execution of the ultrafiltration process, it is convenient according to the invention to maintain the following conditions: The semipermeable membrane should have a high separation threshold, generally between 5000 and 100,000, expressed in the molecular weight of calibration proteins ëtalons) in a neutral buffered environment, the bypass velocity of the latex at the membranes should exceed 0.5 m / s and preferably be between 1 and 2 m / s to avoid clogging of the membranes while limiting the pressure loss in the ultrafilter and the shear for which the latex exposed, the pressure difference between the sides of the membrane should be between 0.1 and 6 bar and preferably between 1.5 and 3 bar, the temperature of the latex should be between 0 and 100 ° C and preferably between 0 and 50 ° C, since the amount of permeate per unit of time decreases as the weight content of dry material of the latex increases, it is convenient to carry out the ultra-filtration at a substantially constant weight. lt and generally between 5 and 70% and preferably between 45 and 55%, possibly after dilution, especially if the viscosity of the latex is very high. In the shutdown of the plant should be followed by a rinse cycle with clean water sufficient to prevent irreversible clogging and destruction of the membranes.

If the latex shows insufficient mechanical stability to undergo ultrafiltration treatment without giving rise to agglomerate formation, work can be done by pre-transferring the latex to an alkaline pH with a value generally between 7.5 and 9.5. At the end of the ultrafiltration, the latex can be concentrated, if desired, to a dry matter content suitable for the intended use.

The invention is described in more detail with the following exemplary embodiments.

Examples 1-14 - Examples 1, 3, 5, 7, 9, 11 and 13 are comparative examples. Examples 2, 4, 6, 8, 10, 12 and 14 are examples according to the invention.

Aqueous coating compositions are prepared and applied to a paper by means of an air knife coating apparatus a coating amount of 20 g / m 2, expressed as dry matter, of each of the indicated compositions. A paper with a weight of 54g / m2 is used according to examples 1-6 and 70g / m2 according to examples 7-14. The paper coated in this way is dried in a tunnel oven at a temperature of 100 ° C and then subjected to calendering comprising four passages in a row between two cylinders under a force of 80 kp / cm.

After drying and calendering, the coated paper is conditioned at a temperature of 20 ° C in an atmosphere with a relative humidity of 65% and then examined for resistance to dry dripping and resistance to dripping in a moist state using the following methods: Resistance to dry dripping : This property is determined by means of an IGT apparatus designed by the "Institut von Grafische Technik" in which the paper is brought into contact with a colored roll whose pressure against the paper is regulated to a selected value and whose speed is increased until the initial onset is observed. napping of the applied coating. The resistance to dry pickling is determined by the speed corresponding to the initial pickling. The printing ink "3805" is used with graded drawing (ä tirant graduê) which is carried in the hands of Etablissements Lorilleux Lefranc.

Resistance to damp napping: This property is also determined by means of a device of the IGT type, but the dyeing is achieved with a test piece of coated paper on which a thin water film has been applied in advance. Moisture resistance in the wet state is determined visually by comparison with other specimens. The color "380l" is used which is carried in the hands of Etablissements Lorilleux Lefranc. The results are expressed with a value between 0 and 10, the value 0 corresponding to a paper which exhibits very poor durability and the value 10 to a paper which exhibits very good durability.

Table I lists for each example the reference designation of the aqueous latex materials used as the binder, the nature of the polymer contained in the latex and the content of water-soluble dissolved compounds in the aqueous phase based on the weight in f of the polymer.

Table I Concerning Reference content of water Type of polymer soluble compounds in relation to the amount of polymer, weight percent Examples 1, 3 and 5 Carboxylated copolymer of butadiene and styrene containing, by weight, 43% butadiene, 53% styrene and 4% ethylenic carboxylic acids 4.7 Examples 2, 4 and 6 Carboxylated copolymer of butadiene and styrene containing, by weight, 43% butadiene, 53% styrene and 4% ethylenic carboxylic acids Examples 7 and 9 Carboxylated polyvinyl acetate containing, by weight by weight, 98% vinyl acetate, 2% ethylenic carboxylic acids Examples 8 and 10 Carboxylated polyvinyl acetate containing, by weight, 98% vinyl acetate and 2% ethylenic carboxylic acid 0.48 Examples 11 and 13 Carboxylated copolymer of vinyl acetate and 2-ethyl- hexyl acrylate containing by weight 88% vinyl acetate, 10% 2-ethylhexyl acrylate and 2% ethylenic carboxylic acid 1.83 Examples 12 and 14 Carboxylated copolymer of vinyl acetate and 2-ethyl hexyl acrylate containing by weight, 88% vinyl acetate, 10% 2-ethylhexyl acrylate and 2% ethylenic carboxylic acid 0.08 The latex materials B, D and F used in the examples according to the invention have been obtained starting from latex A, C and E with a content of 50% by weight of dry material, which is used in the comparative examples, by subjecting the latex materials to ultrafiltration as described below. This treatment was carried out on the latex materials as such in the experiment according to Examples 2, 4 and 6 and on the latex materials which were first treated to a dry matter weight of 30% and a pH value of 8 by adding an ammoniacal aqueous solution in the case of Examples 8, 10, 12. and 14.

The ultrafiltration is carried out in a plant that has an ultrafiltration area of 0.7 m2 equipped with a membrane whose separation threshold amounts to 20,000 and which is operated by Rhone-Poulenc Industries under the designation "Iris 3538", fed with a pump that can emit 6 m3 / h under a pressure of 3 bar. During the ultrafiltration, the dry matter content of the latex is kept constant by means of deionized water.

Table 2 below indicates for each example according to the invention the duration of the ultrafiltration.

Table 2 Duration of ultrafiltration (hours) Examples 2, 4 and 6 9 Examples 8 and 10 8 Examples 12 and 14 13 At the end of the ultrafiltration, the latex materials D and F are concentrated to the initial content of 50% by weight of dry matter.

After emptying, rinse the device with plenty of water. It can be determined that the clogging of the membranes is 0. Tables 3 and 4 below indicate the nature and weight content of solids in the coating compositions for each example. Furthermore, the weight content of dry material to which they are at a pH value of 8.5 by the addition of ammonia set coating compositions are adjusted.

Table 3 Example 1 2 3 4 5 4 6 Kaolin - 100 100 100 10 100 100 100 Sodium hexamate phosphate 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Carboxymethylcellulose 0.3 0.3 - - - - Starch - - 6 6 - - Polyvinyl alcohol - - - - 2 2 Latex A 12 - 8 - 10 - Latex B - 12 - 8 - 10 Weight content of dry 48 48 48 48 52 52 material (%) Table 4 Example 1 7 8 9 10 11 12 É 13 14 Kaolin l00 100 100 l00 100 100 100 100 Sodium pyrophosphate 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Polyvinyl alcohol ll 2 2 ll 2 2 Latex C 12 10 Latex ni 12 10 Latex E _ 12 10 Latex F 12 10 Weight content of dry matter (%) 50 50 50 50 50 50 50 50 ll Tables 5 and 6 give the results as examples. \ obtained at each Table 5 Example 1 2 3 4 5 6 Resistance to dry snatching 87 71 50 61 62 63 (cm / s) Resistance to wet pickling 4 7 4 6 5 6 Table 6 Example 7 8 9 10 ll 12 13 Resistance to dry - napping (cm / s) 42 43 42 43 42 45 52 Resistance to wet napping 3 5,5 5 6 5,5 7 8 It appears that the latex materials B, D and F, which are used as adhesives according to the invention, gave coated papers which exhibited a resistance to dry napping and resistance to wet napping which was superior to the properties obtained with paper coated with the aid of aqueous compositions containing the latex materials A, C and E.

Claims (4)

'/ .- 8U46Ub 9 m Patent claim i Binder based on an aqueous latex of a synthetic polymer for the preparation of aqueous compositions for coating paper, cardboard and cardboard for printing, characterized in that the content of water-soluble compounds dissolved in the aqueous phase is less than 0.5% by weight in relation to the amount of polymer, by removing water-soluble compounds by ultrafiltration through a semipermeable membrane, with a separation threshold between 5,000 and 100,000, expressed as the molecular weight of calibration proteins in a neutral buffered environment? Binder according to Claim 1, characterized in that the polymer is selected from the group consisting of copolymers of styrene and butadiene, carboxylated copolymers of butadiene and styrene, polyvinyl acetate, carboxylated polyvinyl acetate, copolymers of vinyl acetate and alkyl acrylate, carboxylates of vinyl acetate and alkyl acrylate. Binder according to Claim 1 or 2, characterized in that the ultrafiltration is carried out at a weight content in the latex of dry material which is substantially constant and is between 5 and 70% and preferably between 45 and 55%. Binder according to Claim 1 or 2, characterized in that the latex is concentrated at the end of the ultrafiltration to a dry material content suitable for the intended use.